Various apparatuses have been proposed as the above fuel supply apparatuses.
For example, a fuel supply apparatus 100 disclosed in Patent Document 1 includes a fuel tank 101 and a fuel pump 102 disposed within the fuel tank 101 as shown in FIG. 12. Fuel within the fuel tank 101 is pressurized by the fuel pump 102 and passes through a fuel filter 103, and thereafter, its pressure is adjusted to a predetermined pressure by a pressure adjusting mechanism 110, and the fuel is then supplied to each of injectors 105 via a branch pipe section 104. Then, the fuel is injected into each of cylinders (not shown) from each injector 105.
A pressure regulator 112 of the pressure adjusting mechanism 110 is provided with a diaphragm (not shown) that separates a control pressure chamber 112c and a fuel pressure adjusting chamber 112f from each other, and a valve body (not shown) for returning (releasing) the fuel within the fuel pressure adjusting chamber 112f to the inside of the fuel tank 101 is connected to the diaphragm. In addition, the pressure adjusting mechanism 110 has a pressure control valve 117 on the inlet side of the control pressure chamber 112c of the pressure regulator 112, and the pressure control valve 117 can open and close based on a signal from a control unit 120.
When the engine is started or in other occasions, the pressure adjusting mechanism 110 supplies the fuel into the control pressure chamber 112c by opening the pressure control valve 117, in order to increase the pressure within the control pressure chamber 112c by the pressure of the supplied fuel. This causes the diaphragm to be flexed and the valve body narrows the flow passage, so that flow passage resistance increases. As a result, the fuel pressure within the fuel pressure adjusting chamber 112f increases, and the fuel pressure within the branch pipe section 104 communicating with the fuel pressure adjusting chamber 112f increases. Thus, because the fuel pressure supplied to each injector 105 becomes high, atomization of the injected fuel is enhanced and the startability of the engine is improved. Further, after the engine has started, the pressure control valve 117 is closed to lower the pressure within the control pressure chamber 112c. This causes the diaphragm to flex in the opposite direction, so that the valve body broadens the flow passage to decrease the flow passage resistance. As a result, the fuel pressure within the fuel pressure adjusting chamber 112f decreases, and the fuel pressure within the branch pipe section 104 communicating with the fuel pressure adjusting chamber 112f decreases. Thus, because the fuel pressure supplied to each injector 105 becomes low, it is possible to reduce the load on the fuel pump 102, etc.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2001-90624
The pressure adjusting mechanism 110 of the fuel supply apparatus 100 described above is configured to increase the pressure of the fuel supplied to each injector 105 in order to improve the startability of the engine. Therefore, it may be considered to quickly lower the pressure of the fuel after the engine has started. However, for example, when the engine is restarted on a high-temperature condition, vapor may be produced within the fuel due to decrease in the fuel pressure even after starting the engine, and therefore, there is a possibility that the amount of fuel injected from the injectors fluctuates to cause unstable idling rotational speed.
In addition, with the pressure adjusting mechanism 110 of the fuel supply apparatus 100 described above, in order to bring the fuel pressure supplied to the injectors 105 to be a high pressure, the pressure control valve 117 is opened for communicating the control pressure chamber 112c of the pressure regulator 112 and the outlet region of the fuel filter 103 with each other. Therefore, if the fuel pressure within the fuel pressure adjusting chamber 112f increases in response to the pressure within the control pressure chamber 112c, the fuel pressure within the fuel pressure adjusting chamber 112f is applied to the inside of the control pressure chamber 112c via the pressure control valve 117, resulting in increase of the pressure within the control pressure chamber 112c. Thus, the pressure within the control pressure chamber 112c gradually increases, and the fuel pressure within the fuel pressure adjusting chamber 112f increases in a proportional manner, so that the fuel pressure supplied to the injectors 105 increases.
Further, on the condition that the fuel is supplied into the control pressure chamber 112c of the pressure regulator 112 due to opening of the pressure control valve 117, i.e., on the condition that the diaphragm is flexed to narrow the flow passage by the valve body, for example, if the amount of flow rate of the fuel flowing through the flow passage of the valve body gradually increases, the valve body and the diaphragm move as the flow rate increases, and therefore, the fuel pressure within the control pressure chamber 112c and the fuel pressure adjusting chamber 112f increases. As a result, the pressure of the fuel supplied to each injector 105 increases.
Because the pressure of the fuel supplied to the injectors 105 affects the fuel injection performance of the injectors 105, fluctuation is not desirable.
Thus, there is a need in the art for fuel supply apparatuses that can inhibit fluctuation in amount of fuel injected from an injector, and to inhibit change of the fuel pressure when the pressure of fuel supplied to the injector is changed to a high pressure.